Saturn's Mystery North Pole

In November 1980, planetary scientists eagerly examined transmissions received from the Voyager 1 spacecraft as it sped past Saturn. And with good reason! Amid those transmissions was the first image of Saturn’s North Pole – a region that’s virtually impossible to see from Earth, and, depending on the degree by which Saturn is tilted, can be cloaked in darkness for up to 15 years at a time (and you thought your last winter was never going to end).

What those scientists saw, and later missions confirmed, was a decidedly bizarre feature in the gas giant’s atmosphere directly above the North Pole: a 15,000-mile-wide hexagon.

The hexagons naturally occur all over the place: basalt columns; beehive honeycombs; snowflakes; and even molecules offer some examples. Unfortunately the processes responsible for these formations by no means explain the feature on Saturn. In fact, the planet’s thick atmosphere is one of the last places experts were prepared to find such a geometric oddity – even its South Pole has a reassuringly circular, terrifyingly enormous hurricane churning up the clouds.

So why is it there? Besides dropping Jodie Foster – or, ideally, Matthew McConaughey – into the middle of the 60-mile-deep hexagon and seeing where she goes, a slightly less exciting experiment conducted by the Niels Bohr Institute in Denmark provided some intriguing results. And by slightly less exciting, we mean they stirred a bucket of water. What they found was that at certain speeds the water flow would interact with the edges of the cylindrical container to create rotating polygons with up to 6 corners.

As you may have already guessed, the experiment has a long way to go before it explains Saturn’s hexagon. For one thing, a colossal bucket isn’t sitting at the North Pole to provide distinct boundaries for the planet’s many complex layers of clouds to interact. Scientists have yet to figure out precisely how Saturn is creating a similar result with its multifaceted toolkit of jet streams and waves. Perhaps a more relevant explanation may be found in satellite observations of Hurricane Isabel (PDF) from 2003, wherein the storm’s eyewall alternated between pentagonal and hexagonal formations through unique combinations of smaller rotational features called mesovortices; showing us that even home grown storms can test and inevitably improve our equations of motion.

VIEW - Cassini Equinox Mission Comparison

In the early 1980s, the Voyager probe spotted the strange feature, which rotates about a fixed axis centered on Saturn’s north pole, and it is still going strong. The Voyager craft was state-of-art for its day; of course, the technology on board the newer Cassini spacecraft, which captured the short movie (below) allows much more detail.

"The longevity of the hexagon makes this something special, given that weather on Earth lasts on the order of weeks," said Kunio Sayanagi, a Cassini imaging team associate at the California Institute of Technology. "It's a puzzler on par with the strange weather conditions that give rise to the long-lived Great Red Spot of Jupiter."

Cassini has been lingering in a Saturn orbit for the past five years. It has helped science learn much about the ringed giant and its moons, such as Encelaudus having ice geysers, and the existence of more faint rings about the planet.

The north pole of Saturn was cloaked in night for 15 years, so when Cassini arrived in 2004 it had to “wait” to get the best images of the feature. Light began to shine on the north pole in January of 2009 as Saturn’s northern hemisphere spring began. Infrared sensors aboard Cassini had indicated the stationary nature of the “hex” and its extension high into the Saturnian air for several years prior to that. Now, visible light studies are allowing even greater probing of this celestial mystery.

There are lots of questions and few answers about this hexagon, which is estimated to be about 15,000 miles across. The prevailing theory; it’s caused by jet stream winds. These winds blow at an estimated 220mph, about the same as a vigorous jet (at 34,000 feet) on our planet. Examination of 55 visible images from Cassini also reveal intriguing wave structures at each “corner” of the 6-sided shape.

In this author’s opinion, permanently fixed low-pressure areas, perhaps stationed along some kind of frontal feature (and interacting with magnetic or electrical atmospheric effects?) could offer at least a partial solution to the mystery. Only time will tell. NASA analysis of the winds inside the hexagon “wall” show this is a 60-mile deep area of winds “whipping about the hex like cars on a racetrack”

Of course, it may not be a true hexagon at all; as the data is gathered and analyzed further it may be revealed that the 6-sided appearance is just an optical illusion. An analogy would be the comparison of a low-pixel compared to a high pixel image.

In any case, it will be a while before a confident answer will be known as study of the data continues. Kevin Baines, an atmospheric scientist at NASA's Jet Propulsion Laboratory, says: "Solving these unanswered questions about the hexagon will help us answer basic questions about weather that we're still asking about our own planet."[Source - Examiner.com -NASA.com, Space.com]

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